Fibrinogen is the plasma protein responsible for blood clot formation. Normal fibrinogen is a complex of two chains, out of the α, β and γ chains. About 1% of the total fibrinogen in adult humans contains a variant of a fibrinogen (also termed fib340), known as αE fibrinogen (fib420), which has an extended a chain. The four types of fibrinogen chains, α, β, γ and αE, contain 610, 483, 411 and 866 amino acids, respectively (the numbering based on the Gene-bank database, accessible at ncbi.nlm.nih.gov).
Fibrinogen is not immunogenic within the same species, as attested by the use of pooled fibrin glue for clinical applications. Besides its hemostatic activity, it has been previously demonstrated that fibrin(ogen) elicits cell attachment (haptotactic) and migratory (chemotactic) responses with different cell types including mouse and human fibroblasts (MF and HF), bovine aortic endothelial cells (BAEC) and smooth muscle cells (SMC).
The carboxy terminal sequences, i.e., the C-terminal 30-40 amino acids of the fibrinogen chains, are highly conserved between different species. This region, which is termed FRED (fibrinogen related domain), is present also at the end of the C-terminus domains of some non-fibrin related proteins, such as, tenascins, angiopoietins, and microfibril associated protein 4 (MFA4).
U.S. Pat. Nos. 7,122,620 and 7,148,190 of the inventors of the present invention, incorporated herein by reference, disclose isolated peptides (hereinafter “haptides”) with homologous sequences corresponding to sequences of 19-21 amino acids in the carboxy termini regions of the β, γ and αE chains of fibrinogen (peptides termed cβ, Cγ and CαE respectively), or from other protein comprising regions in the C-termini that are homologous to the fibrinogen sequences of Cβ, preCγ or CαE. These include microfibril-associated protein-4, members of the angiopoietin I and II protein families and tenascins, a family of extracellular proteins. Haptides were shown to induce haptotactic responses in various cultured cell types, mostly of mesenchymal origin, such as HF, BAEC and SMC. Some of the haptides, for example—Cβ, were shown to be rapidly taken up by the cells in a non-saturatable manner. None of the haptides affected the rate of cell proliferation.
There is a recognized need for, and it would be highly advantageous, to design synthetic haptotactic peptides having improved stability which contain an active part of the haptide sequence linked to part of the M-tide that stabilizes it. This does not require the presence of the entire fibrin(ogen) or other proteins containing the haptotactic peptides to attach cells.